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From:   Arnd Bergmann <arnd@kernel.org>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH] powerpc: mark local variables around longjmp as volatile
Date:   Thu, 29 Apr 2021 10:06:38 +0200
Message-Id: <20210429080708.1520360-1-arnd@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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From: Arnd Bergmann <arnd@arndb.de>

gcc-11 points out that modifying local variables next to a
longjmp/setjmp may cause undefined behavior:

arch/powerpc/kexec/crash.c: In function 'crash_kexec_prepare_cpus.constprop':
arch/powerpc/kexec/crash.c:108:22: error: variable 'ncpus' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbere
d]
arch/powerpc/kexec/crash.c:109:13: error: variable 'tries' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbere
d]
arch/powerpc/xmon/xmon.c: In function 'xmon_print_symbol':
arch/powerpc/xmon/xmon.c:3625:21: error: variable 'name' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'stop_spus':
arch/powerpc/xmon/xmon.c:4057:13: error: variable 'i' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'restart_spus':
arch/powerpc/xmon/xmon.c:4098:13: error: variable 'i' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'dump_opal_msglog':
arch/powerpc/xmon/xmon.c:3008:16: error: variable 'pos' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'show_pte':
arch/powerpc/xmon/xmon.c:3207:29: error: variable 'tsk' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'show_tasks':
arch/powerpc/xmon/xmon.c:3302:29: error: variable 'tsk' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'xmon_core':
arch/powerpc/xmon/xmon.c:494:13: error: variable 'cmd' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c:860:21: error: variable 'bp' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c:860:21: error: variable 'bp' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c:492:48: error: argument 'fromipi' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]

According to the documentation, marking these as 'volatile' is
sufficient to avoid the problem, and it shuts up the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/powerpc/kexec/crash.c |  4 ++--
 arch/powerpc/xmon/xmon.c   | 22 +++++++++++-----------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
index 0196d0c211ac..10f997e6bb95 100644
--- a/arch/powerpc/kexec/crash.c
+++ b/arch/powerpc/kexec/crash.c
@@ -105,8 +105,8 @@ void crash_ipi_callback(struct pt_regs *regs)
 static void crash_kexec_prepare_cpus(int cpu)
 {
 	unsigned int msecs;
-	unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */
-	int tries = 0;
+	volatile unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */
+	volatile int tries = 0;
 	int (*old_handler)(struct pt_regs *regs);
 
 	printk(KERN_EMERG "Sending IPI to other CPUs\n");
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index c8173e92f19d..ce0eacf77645 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -489,10 +489,10 @@ static void xmon_touch_watchdogs(void)
 	touch_nmi_watchdog();
 }
 
-static int xmon_core(struct pt_regs *regs, int fromipi)
+static int xmon_core(struct pt_regs *regs, volatile int fromipi)
 {
-	int cmd = 0;
-	struct bpt *bp;
+	volatile int cmd = 0;
+	struct bpt *volatile bp;
 	long recurse_jmp[JMP_BUF_LEN];
 	bool locked_down;
 	unsigned long offset;
@@ -857,7 +857,7 @@ static inline void force_enable_xmon(void)
 static struct bpt *at_breakpoint(unsigned long pc)
 {
 	int i;
-	struct bpt *bp;
+	struct bpt *volatile bp;
 
 	bp = bpts;
 	for (i = 0; i < NBPTS; ++i, ++bp)
@@ -3005,7 +3005,7 @@ static void dump_opal_msglog(void)
 {
 	unsigned char buf[128];
 	ssize_t res;
-	loff_t pos = 0;
+	volatile loff_t pos = 0;
 
 	if (!firmware_has_feature(FW_FEATURE_OPAL)) {
 		printf("Machine is not running OPAL firmware.\n");
@@ -3160,7 +3160,7 @@ memzcan(void)
 		printf("%.8lx\n", a - mskip);
 }
 
-static void show_task(struct task_struct *tsk)
+static void show_task(struct task_struct *volatile tsk)
 {
 	char state;
 
@@ -3204,7 +3204,7 @@ static void format_pte(void *ptep, unsigned long pte)
 static void show_pte(unsigned long addr)
 {
 	unsigned long tskv = 0;
-	struct task_struct *tsk = NULL;
+	struct task_struct *volatile tsk = NULL;
 	struct mm_struct *mm;
 	pgd_t *pgdp;
 	p4d_t *p4dp;
@@ -3299,7 +3299,7 @@ static void show_pte(unsigned long addr)
 static void show_tasks(void)
 {
 	unsigned long tskv;
-	struct task_struct *tsk = NULL;
+	struct task_struct *volatile tsk = NULL;
 
 	printf("     task_struct     ->thread.ksp    ->thread.regs    PID   PPID S  P CMD\n");
 
@@ -3622,7 +3622,7 @@ static void xmon_print_symbol(unsigned long address, const char *mid,
 			      const char *after)
 {
 	char *modname;
-	const char *name = NULL;
+	const char *volatile name = NULL;
 	unsigned long offset, size;
 
 	printf(REG, address);
@@ -4054,7 +4054,7 @@ void xmon_register_spus(struct list_head *list)
 static void stop_spus(void)
 {
 	struct spu *spu;
-	int i;
+	volatile int i;
 	u64 tmp;
 
 	for (i = 0; i < XMON_NUM_SPUS; i++) {
@@ -4095,7 +4095,7 @@ static void stop_spus(void)
 static void restart_spus(void)
 {
 	struct spu *spu;
-	int i;
+	volatile int i;
 
 	for (i = 0; i < XMON_NUM_SPUS; i++) {
 		if (!spu_info[i].spu)
-- 
2.29.2